Method of forming carbonaceous protective coatings on titanium and zirconium



United htates Patent METHOD OF FORMING CARBONACEOUS PRO- TEC'IIIJVECOATINGS ON TITANIUM AND ZIR- CON M Frank X. McCawley, Cheverly, Md.,assignor to Chicago Development Corporation, Riverdale, Md., acorporation of Delaware N 0 Drawing. Application November 5, 1957 SerialNo. 694,504

1 Claim. (Cl. 148-131) This invention relates to protective coatings ontitanium and zirconium and their alloys. It relates particularly to suchcoatings for protection of the metals and alloys during heat treatmentand working.

In my copending application, Serial No. 668,771, filed June 25, 1957, Ihave disclosed that carbide coatings are effective means for theprotection of titanium alloys at high temperatures. I have disclosed inthat application several methods of producing such coatings. The presentinvention is concerned with improved methods of producing such coatings.

The improved method of this invention consists in heating the metal partto be protected in a pure hydrocarbon vapor in a temperature range of7501000 C. The metal in this treatment forms a thin coating of carbidecovered with a layer of carbon.

The metal or alloy treated in this way is protected from oxidation whenheated in air to temperatures in the range 750-900 C. To preventcontamination of the surface, the hydrocarbon vapor must be free fromoxygen, nitrogen or metallic impurities.

Having now described my invention in its more general aspects, I willillustrate it by examples.

Example I In this example, I take pure titanium containing .025 oxygen;I heat for 30 minutes to 800 C. in an atmosphere of butane, and cool inthe gas. I now heat this material in air at 850 C. for 1 hour. Forcomparison, I take an untreated piece of the same titanium and heat itin air at 850 C. for 1 hour. I then determine the oxygen penetrationinto the titanium surface in the two pieces. The results follow:

0; Content Mlle from Surface Coated Uncoated I a .025 .042 a 025 035 m025 030 12 025 028 14 025 026 16 .025 .025 18 .025 .025 20 025 0252,865,797 Patented Dec. 23, 1958 It will be seen that the carbidecoating restricts oxygen absorption a layer at the surface less than 4mils thick.

Example 11 In this example, I take pure zirconium and proceed as inExample I except that I use pure methane at 750 C. in the coatingoperation. After heating in air at 900 C. for 1 hour, I find that theoxygen penetration in the heated piece is limited to 4 mils, while inthe untreated piece oxygen has penetrated for 20 mils.

Example 111 Example IV In this example, I proceed as in Example I exceptthat the alloy is titanium, 10% aluminum. I heat to 800 C. in pureethyline for 20 minutes and cool in the gas. I now heat this material inair at 850 C. for 1 hour. I find that oxygen penetration has beenlimited to a surface zone 3 mils thick.

What is claimed is:

The method of treating a metal mass selected from the group consistingof titanium, titanium alloys, zirconium and zirconium alloys in anoxidizing atmosphere at 6001100 0., Without oxygen penetration to adepth of more than about 4 mils which consists in first heating in apure hydrocarbon vapor at 7501000 C. for 10-30 minutes.

References Cited in the file of this patent Hanzel: Metal Progress,March 1954, pages 91, 92. Griest et al.: American Society for MetalsTransactions, vol. 46, 1954, page 267.

